Handlebar stems using wedge shaped expander nut to secure a stem quill tube within the front fork steering tube of a bicycle have been known and used for many years. A relatively conventional stem structure 10 is depicted in exposed side view in FIG. 1. A steering tube 12 is mounted upon bearings 14 within the bicycle frame head tube 16. The quill tube 18 of the stem 10 is mounted within the steering tube 12, is hollow and includes, upon an exposed end 20, a cap 22 having a hole 24 drilled therethrough for accepting a long bolt 26. The threaded end 28 of the screw 26 engages the center of a wedge shaped expander nut 28 positioned within the steering tube 12. The quill tube 18, expander nut 28 and steering tube 12 fit together snugly so that when the elongated screw 26 is tightened, the expander nut 28 is urged to move axially which, by virtue of the wedged interconnection of the quill tube 18 and expander nut 28, causes radially opposing displacement of the expander nut versus the quill tube. As such, the extended ends 30, 32 of each of the expander nut 28 and quill tube 18 become forced against diametrically opposed inner walls of the steering tube 12. This force prevents both radial and axial movement of the stem 10 relative to the steering tube 12.
The advantage of an expander nut structure as shown in FIG. 1 is that the quill tube 18 may be universally raised and lowered and rotationally positioned relative to the steering tube 12. A stem structure such as FIG. 1 holds the disadvantage in that the bolt 26 must be as long as the quill tube itself. This is because there is no position upon the quill tube that adequately supports the axial pressure generated by the elongated bolts head 36 when tightened except the upper rim 34 of the quill tube 12. Thus, a cap 22 carrying the bolt must be used to abut the upper rim 34. Any attempt to recess the cap (22) within the inner surface of the quill tube requires either the use of complex, weight adding and potentially weakening welding processes. Otherwise, positioning a recessed bolt head support platform within the quill tube requires inclusion of a platform engaging shoulder within the inner surface of the quill tube that either adds significantly to weight by adding a thicker lower inner wall with a ledge or, alternatively, requires removal of part of the upper inner wall to construct the ledge that may overly thin part of the quill tube inner wall.
One alternative to forming a cap ledge in the quill tube itself is to use of a simple insert that is fully disposed within the quill tube and abuts the expander nut face, thus acting as a platform against which the screw head may rest. Such an insert, however, may not prove axially secure enough to maintain sufficient compressive and rotational pressure relative to the expander nut. Alternatively, pinning or otherwise radially securing this kind of insert to the walls of the quill tube defeats the purpose of such a structure by adding significant weight and, again, weakening the quill tube wall.
As such, it has generally been necessary to continue to include the elongated bolt 26 as shown in FIG. 1 in most expander nut structures. This bolt, however, significantly adds to the overall quill tube weight since it must be constructed from solid hardened steel or similarly dense materials.